Diagnosing acromegaly typically takes years, in part because the physical changes it causes develop so gradually that patients and doctors alike can miss them. A large study of acromegaly patients found a median delay of 3 years from symptom onset to diagnosis, with 40% of patients waiting more than 5 years. The process involves recognizing subtle physical changes, running specific blood tests, and then locating the source of excess growth hormone with imaging.
Physical Signs That Prompt Testing
Acromegaly doesn’t announce itself with a single dramatic symptom. Instead, a cluster of changes accumulates over time, and it’s often the combination that raises suspicion. The features most likely to trigger a workup include enlargement of the hands and feet (many patients notice their rings or shoes no longer fit), changes in facial structure such as a more prominent brow, widened nose, thickened lips, and a protruding jaw with widening spaces between the teeth. An enlarged tongue is also common.
Beyond the visible changes, certain medical conditions show up at unusually high rates in people with acromegaly and can serve as diagnostic clues. Obstructive sleep apnea, carpal tunnel syndrome, and new-onset type 2 diabetes, particularly in someone without the usual risk factors, all warrant consideration. When two or three of these features appear together, blood testing is the next step.
IGF-1: The First Blood Test
The primary screening tool is a blood test measuring insulin-like growth factor 1, or IGF-1. Your body produces IGF-1 in the liver in response to growth hormone, and because IGF-1 levels stay relatively stable throughout the day (unlike growth hormone itself, which spikes and dips), a single blood draw gives a reliable picture. In one study of confirmed acromegaly patients, IGF-1 was elevated in every single case before treatment, making it an extremely sensitive screening marker.
The critical detail with IGF-1 is that “normal” depends on your age and sex. IGF-1 naturally peaks during puberty, around age 12 to 13 in girls and 15 in boys, then steadily declines for the rest of life. A level that would be perfectly normal for a teenager could be a red flag in a 50-year-old. Labs report results alongside age-adjusted reference ranges for this reason, and the result is often converted to a standardized score that accounts for these differences. If your IGF-1 comes back clearly elevated for your age, that alone is often enough to establish the diagnosis in someone with classic physical features.
The Glucose Suppression Test
When IGF-1 results are borderline or the clinical picture isn’t clear-cut, a confirmatory test is needed. This is the oral glucose tolerance test, adapted specifically for acromegaly. You drink a solution containing 75 grams of glucose, and your blood is drawn at intervals over the next two hours to measure growth hormone levels.
In a healthy person, the sugar load tells the pituitary gland to dial back growth hormone production. Growth hormone should drop below 1 microgram per liter. In acromegaly, the pituitary tumor keeps producing growth hormone regardless of the glucose signal, so levels stay stubbornly high. Some newer, more sensitive lab assays can detect growth hormone at very low concentrations, and a stricter cutoff of 0.4 micrograms per liter has been proposed. However, the Endocrine Society’s clinical practice guideline maintains the 1 microgram per liter threshold because many standard assays aren’t accurate enough at those very low levels.
This test isn’t just a formality. It catches cases where IGF-1 is only modestly elevated, which can happen early in the disease when physical signs are still subtle.
Conditions That Complicate the Results
Several situations can make IGF-1 or growth hormone results misleading. Pregnancy, puberty, estrogen-based medications, chronic kidney disease, liver disease, and untreated hypothyroidism all affect either how much growth hormone your body makes or how it gets processed. Liver disease is especially relevant because the liver is where IGF-1 is produced: a damaged liver may fail to make enough IGF-1 even when growth hormone is running high, creating a falsely reassuring result. Conversely, poorly controlled diabetes can complicate the glucose suppression test itself.
Doctors evaluating ambiguous results will look at the full clinical picture and may repeat testing after addressing any confounding conditions.
Finding the Tumor With MRI
Once blood tests confirm excess growth hormone, a pituitary MRI locates the source. In the vast majority of cases, it’s a benign tumor (adenoma) in the pituitary gland at the base of the brain. These tumors are classified by size: those 10 millimeters or smaller are called microadenomas, and those larger than 10 millimeters are macroadenomas.
A study of 297 acromegaly patients found that tumor appearance on MRI carries useful information beyond just size. Tumors that appear dark on a specific type of MRI sequence (T2-weighted imaging) tend to be smaller, are associated with higher IGF-1 levels, and are less likely to invade surrounding structures. Tumors that appear bright or similar in shade to normal brain tissue are more often larger, and roughly half of those over 11 millimeters showed invasion into the cavernous sinus, a critical area near the pituitary. About 18% of all patients in the study had compression of the optic chiasm, the crossroads of the optic nerves, which can affect peripheral vision.
The MRI findings help determine treatment approach and surgical complexity, making the imaging step essential even after blood tests have already confirmed the diagnosis.
When No Pituitary Tumor Is Found
In rare cases, blood tests clearly show excess growth hormone, but the pituitary MRI looks normal or shows only enlargement of the gland without a distinct tumor. This raises the possibility of ectopic acromegaly, where a tumor somewhere else in the body is producing growth hormone-releasing hormone (GHRH), which in turn overstimulates the pituitary. Chronic GHRH stimulation causes the pituitary to enlarge in a way that can be mistaken for a tumor on MRI, or it may look unremarkable altogether.
The key diagnostic step here is measuring GHRH levels in the blood. Elevated GHRH points toward a source outside the pituitary, most commonly a tumor in the lungs or pancreas. Identifying this distinction matters enormously because the treatment is entirely different: removing the GHRH-producing tumor rather than operating on the pituitary itself.
The Typical Diagnostic Pathway
In practice, the sequence follows a predictable order. A doctor notices suspicious physical changes or a pattern of related conditions, orders an IGF-1 blood test matched to age-appropriate reference ranges, and if results are elevated, either confirms the diagnosis based on strong clinical evidence or proceeds to the glucose suppression test. Once confirmed, a pituitary MRI maps the tumor’s size, location, and relationship to nearby structures. If no pituitary tumor is found, GHRH testing helps identify whether the excess growth hormone is being driven from elsewhere in the body.
The entire workup can be completed within a few weeks once suspicion is raised. The real bottleneck is that initial recognition, which accounts for the years-long delay most patients experience. Awareness of the physical signs, particularly when they cluster together, is what gets the process started.